This invention relates to a document of value consisting of a substrate of predetermined surface area with a printed image visible to the naked eye and a marking in the form of characters, patterns or the like at least partly superimposed on the printed image, said marking having a given regularity which allows manipulations of the document to be recognized. The term xe2x80x9cdocument of valuexe2x80x9d will be used in the following text as a general term for all kinds of documents of value, i.e. vouchers, tickets, identity cards, bank notes, securities, shares and the like.
Vouchers or tickets to be used for several events, such as public transport tickets to be used for several journeys, usually consist of a strip-shaped paper carrier divided into a plurality of likewise strip-shaped fields. One field corresponds to a certain amount of money. The fare for using public transport is frequently a multiple of this amount so that the money value of several fields is required for one journey. In order not to have to cancel each field singly, it suffices in known systems to cancel the last field, in the given order, of the fields to be canceled. The fields therebefore which are not directly canceled are thereby deemed canceled as well. This procedure means that in completely canceled tickets some of the single fields are always uncanceled. If these fields are cut out of different canceled tickets, they can be assembled into an apparently new, unused ticket.
In order to prevent such forgeries it has been proposed in DE 32 16 485 C1 to subject the tickets during production to an additional printing operation in which a continuous wave-line pattern is applied to the tickets. This is done on the paper web before it is cut into the individual tickets. For the additional printing operation one uses a printing cylinder whose circumference is a nonintegral multiple of the ticket length so that the wave-line pattern extending continually within a ticket is somewhat offset from the wave-line pattern of the next ticket. This prevents uncanceled fields from being indiscriminately lined up since the wave line normally has discontinuities at the transitions between fields due to the different tickets. To simulate an authentic ticket a potential forger would thus have to make sure the wave lines of the individual fields join up seamlessly. There is little probability of a forger having the suitable fields available.
However, the advantages of the method known from DE 32 16 485 C1 are only effective in the case of a visual check. If such security patterns are to be tested by machine this would require an effort in measurement technology which is unjustified in many cases, since it would involve elaborate calculating processes making the method uneconomical for many applications.
The invention is therefore based on the problem of providing a document of value whose authenticity and intactness can be tested relatively simply by machine.
The solution to this problem results from the machine-readable features of the present invention, including several different embodiments.
The invention starts out from the basic idea that one can recognize forgeries and specific falsifications of documents by testing the presence and defined distribution of machine readable feature substances preferably unrecognizable without technical aids. The assembly of new authentic documents from fragments of different authentic documents is additionally impeded if the distribution on the document is effected in coded form and the coded information is varied at a sufficiently low repetition rate from document to document of a series of documents and/or from partial area to partial area of a document. The control information of the documents is checked either via defined mathematical relations or with reference to data records stored in specific data bases.
According to the invention the document of value has a marking represented by means of a feature substance and extending over the predominant part of the document in order to permit not only the authenticity of the document but also the completeness of the document material to be machine readable. The distribution of the feature substance over the surface of the document makes gaps or added partial elements of other authentic documents recognizable as disturbances.
It is known from the prior art to provide documents of value with feature substances to permit their authenticity to be detected by a machine (U.S. Pat. No. 4,255,652). However, the feature substance is not applied here so as to extend over the total or the predominant part of the surface, so that it is possible to manipulate unmarked areas or replace them by forgeries. In addition, all documents of a series have the same marking so that manipulations by combining partial elements of authentic documents of a series are unrecognizable as long as the visible printed image is retained.
In a preferred embodiment, the document of value consists of a strip-shaped paper carrier subdivided into likewise strip-shaped funds-equivalent partial areas preferably extending transversely to the longitudinal extension of the document. These partial area are defined by a printed image visible to the naked eye. Moreover, the document has a linearly executed marking consisting of a machine readable feature substance preferably invisible when viewed without aids, said marking being at least partly superimposed on the visible printed image and extending over the predominant part of the document. These marking lines preferably extend obliquely to the cancelable funds-equivalent strips given by the normal printed image and constitute a coding.
When the document of value is checked, the authenticity of the document material can be detected via the presence of the right feature substance. The coding contents additionally permit inferences to be drawn about the completeness of the document material. If the read information on a document to be tested does not match the given coded information, this indicates that parts of the original document are either completely lacking or were replaced by forgeries or parts of other authentic documents.
The coding moreover offers the advantage that a large amount of testable information can be stored. Thus, the coding can contain for example information on the nature or the intended use of the document, which can be of benefit for swift machine processing of the documents.
In the above-described embodiment, the information contained in the coding is the same for all partial areas. According to a further embodiment, it is also possible to provide groups of partial areas or each individual partial area with a different coding. However, at least the codings of adjacent partial areas preferably have a mathematical relationship to each other. In this case the marking is composed of a plurality of different information parts, which further heightens the protection from forgery since it increases the effort a potential forger must expend in order to successfully combine parts of other authentic documents with the document being manipulated.
Additional protection from forgery arises if the marking varies from document to document at least at a certain repetition rate. During production of documents of value in endless format this can be effected in a very simple way by applying the marking or machine-readable feature substance with the aid of a special printing cylinder whose circumference corresponds to a nonintegral multiple of the document extension, the repetition rate being determinable via the circumference of the cylinder. This permits the content or form of the marking to be identical for all documents, while the offset produces an individualization via the position of the feature substance at least for a series of consecutive documents.
In order to attain the same goal in sheet printing one must produce a plurality of printing plates, depending on the desired repetition rate, which are provided in the area of each copy with a marking pattern offset from the preceding copy. Alternatively it is of course also possible to predetermine a plurality of different marking patterns so that a more or less low repetition rate occurs depending on the number of given marking patterns.
Machine reading of the inventive documents of value is preferably done in two stages. In a first step one can check whether the printed image visible to the naked eye corresponds to that of an authentic document. This can be done with the aid of known pattern recognition methods by comparing the scanned printed image with a reference pattern stored in the machine. If there is no agreement between printed image and reference pattern, the document is rejected. If comparison is positive, the document is scanned in a second step with a sensor sensitive to the particular physical property of the feature substance, and the distribution of the feature substance on the document detected. The document can be scanned all over or only along a predetermined characteristic measuring track. The detected signal permits inferences to be drawn about the authenticity and completeness of the document. If no signal corresponding to the given feature substance was detected at any place on the document, it is a total forgery, for example the color copy of an original document. Otherwise one has a document at least partly consisting of authentic document material.
If the measuring signal additionally reflects the given arrangement of the feature substance, the document consists of authentic document material which was not manipulated. In this case one has an original document. If the measuring signal contains jumps or discontinuities which do not match the original marking, the document is manipulated. If for example whole areas of the original marking pattern are totally lacking, a part of the document was replaced by a false area, for example one produced by color copying. However, if some areas of the line pattern are lacking in the scanning signal and additional signals occur at unexpected places, this is a sign that a plurality of authentic documents were combined into a forgery which would have been classified as an original document when viewed strictly visually.
However, the visible printed pattern and the machine-readable feature substance also can be checked simultaneously or as a function of each other. For example, one can check whether there is a given correlation between certain printed patterns of the printed image visible to the naked eye and the distribution of the feature substance.
Feature substances that can be used are luminescent, electroconductive, magnetic substances or substances with other mechanically testable properties. However, the machine-readable feature substance is preferably selected so as not to appear visually. That is, one uses substances which either are transparent in the visible spectral region or have a body color corresponding to the background. In this case the marking is advantageously disposed under the printed image visible to the naked eye. However, it is also conceivable to use a machine-readable feature substance with a special body color and integrate it into the visible printed image.
The machine-readable feature substance can be applied for example by usual printing processes, the feature substance serving as the colorant either alone or together with other coloring pigments. The machine-readable feature substance need of course not necessarily be applied linearly. The machine-readable feature substance can also be distributed according to a given mathematical algorithm. Alternatively, it is also possible to apply the machine-readable feature substance as a binary code or in the form of a special pattern. Alternatively, the coding or pattern can also be disposed on the document several times.